GDT:Straightness
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| Symbol | Straightness |
|---|---|
| Type | Form |
| Category | Form |
| Standard | ASME Y14.5 |
| Author | Admin |
| Datums | None |
| Modifiers | Diameter (feature of size), ST (statistical tolerance, where allowed) |
| Tolerance zone | Two parallel lines (surface line element) or a cylindrical zone (axis/feature of size) |
| Image | |
| Common mistakes | Using datums in the FCF; applying straightness to a pattern; missing diameter on a cylindrical feature |
| Related | F4:Straightness Validation |
Summary
Straightness controls the form of a line element or the axis of a feature of size. It limits how far the element or axis can deviate from a perfect straight line.
Definition
For a surface line element, the tolerance zone is two parallel lines separated by the tolerance value. For a feature of size, the tolerance zone is a cylindrical zone around the axis.
When to use it
Use straightness when you need to control form without reference to datums, such as keeping a shaft straight or controlling a line element on a surface.
Examples
Example: Surface line element straightness
Straightness applied to a surface line element with no datum references.
Example: Cylindrical feature of size straightness
Straightness applied to a shaft axis using the diameter modifier.
Common mistakes
- Adding datum references to a straightness FCF.
- Applying straightness to a pattern.
- Omitting the diameter modifier for a cylindrical feature of size.